动态编译 Java 文件 与 动态加载 Java 类

原文：http://hi.baidu.com/helloween0809/blog/item/709c8126e7edb2148a82a12e.html

动态编译java文件 动态加载java类 动态执行java类的main方法。

动态编译需要加载 JDK/lib/tools.jar

下面是代码：

/*
 * IBM Confidential
 *
 * OCO Source Materials
 *
 * #ID# IBM CRL Supply Chain Management Research
 *
 * (C) Copyright IBM Corp. 2005, 2006
 *
 * The source code for this program is not published or otherwise divested of
 * its trade secrets.
 *
 */
 package test;

import java.io.File;
 import java.io.FileOutputStream;
 import java.lang.reflect.Method;
 import java.net.URL;
 import java.net.URLClassLoader;

public class CompileTest
 {

    public static void main(String[] args)
             throws Exception
     {
         String className = "Test";

        File file = new File(new File(System.getProperty("user.dir")),
                 className + ".java");

        StringBuffer sb = new StringBuffer();

        sb.append("public class " + className + " { \r\n");
         sb.append("     public static void main(java.lang.String[] args) throws Exception { \r\n");
         sb.append("         System.out.println(\"This is a class compiled. ");
         sb.append("             class: \" + " + className + ".class.newInstance());     \r\n");
         sb.append("     }   \r\n");
         sb.append("}    \r\n");

        FileOutputStream ous = new FileOutputStream(file);
         ous.write(sb.toString().getBytes());
         ous.close();

        String[] arguments = new String[] { "-d",
                 System.getProperty("user.dir"), className + ".java" };

        // Compile
         int result = com.sun.tools.javac.Main.compile(arguments);

        System.out.println(result == 0 ? "Compiled successly" : "Failed");

        URL classpath = new URL("file:/" + System.getProperty("user.dir") + "/");

        URLClassLoader classLoader = new URLClassLoader(new URL[] { classpath });

        // Load
         Class testClass = classLoader.loadClass(className);

        Method mainMethod = testClass.getMethod("main",
                 new Class[] { String[].class });

        // Invoke main(String[] args)
         System.out.println(mainMethod);

         testClass.newInstance();

        mainMethod.invoke(null, new Object[] { null });

    }
 }

运行结果：

Compiled successly

 public static void Test.main(java.lang.String[]) throws java.lang.Exception

 This is a class compiled.              class: Test@fc9944